In my prior U.S. Pat. No. 5,439,158 disclosed a soldering system having a controlled atmosphere bathing the solder pot and all liquid solder surfaces. In my prior U.S. Pat. No. 5,335,843 I disclosed a spot soldering apparatus which controlled the solder level and immersion of the leads by the meniscus formed by solder in pockets which were filled to overflowing with solder pumped up an adjacent duct. The terminals were then immersed by lowering the PC board until the terminals were a set distance below the meniscus. The pockets must be maintained hot to keep the solder liquid and could damage the printed circuit if they touch. The meniscus formed by the solder at the top of the pocket permits the terminals to be sufficiently immersed in liquid solder without the pocket touching the printed circuit.
In U.S. Pat. No. 5,711,473 the pockets were arranged in a manner similar to that in U.S. Pat. No. 5,335,843 but rather than filling them from adjacent orifices they were filled by raising the level of the solder around the pockets until the pockets were flooded.
In some situations the terminals to be soldered may be scattered around a printed circuit board and require a multiplicity of pockets properly located to solder a number of terminals substantially simultaneously. Other devices may be mounted on the lower surface of the PC board which would be damaged by contact with the solder. The use of pockets ensures that only those terminals and areas intended to be soldered are exposed to the solder. At the same time it is desirable that the pockets, terminals and solder surfaces be protected by an inert atmosphere as efficiently as possible.
In soldering terminals which are close together bridging may occur; that is adjacent terminals may be unintentionally connected by a solder bridge. A process which reduces this tendency is most desirable.
Flux is normally applied to areas to be soldered and the flux may contain volatiles or moisture which is desirably driven off before the terminals are soldered. The current move to volatile free fluxes makes this particularly important since water is now a common ingredient.
Solder balls are also produced in some processes and any reduction in their formation is desirable.